Master a bar game
Be it dominating darts like a British boozehound, making Minnesota Fats look like an amateur pool shark, or running a shuffleboard table like a master tactician, being really, really good at a bar game is essential for any bar-goer's repertoire. It's also really fun when you realize you can dupe strangers out of dollars because you're good at making a ring on a string land on a nail. And no, board games don't count.
Troll the jukebox
If it has Gotye, play it three times. Blame your friend. But no matter what, endure it all like every other poor soul in the bar waiting for the sweet release of… dammit. It's Gotye again, isn't it?
Buy a round for a homeless person
A nice one round. And sit and talk as they enjoy it so nobody treats them poorly for being in the bar. A to-go meal is icing on the cake.
Give a showstopping toast to a room full of strangers
Not some bullshit ancient Gaelic thing you read about on the internet. The kind of toast you might give at a wedding to a crowd of loved ones.
Play on a bar's intramural team
Make yourself part of the portrait on the wall when the kickball/softball/soccer team gets a participation plaque, and thus ensure your own immortality.